1. Field of the Invention
The present invention relates to the field of topical glaucoma therapy. More particularly, this invention relates to certain fatty acid salts of 1-{4-[2-(cyclopropylmethoxy)-ethyl]-phenoxy}-3-isopropylamino-propan-2-ol, which is also known as betaxolol. This compound is a known antiglaucoma agent. The use of this compound to treat glaucoma is described in U.S. Pat. No. 4,342,783; the entire contents of this patent are hereby incorporated in the present specification by reference. The structural formula of this compound and its method of preparation are described in U.S. Pat. No. 4,252,984, the entire contents of which are incorporated herein by reference. The hydrochloride salt of this compound is the active ingredient in BETOPTIC.RTM., a topical ophthalmic preparation currently used in the treatment of glaucoma.
Betaxolol is a cardioselective, beta-adrenergic blocking agent. The cardioselectivity of this compound is a significant advantage in the treatment of glaucoma, because the incidence of pulmonary side effects with this compound is significantly less than with other known beta-blockers used in the topical treatment of glaucoma.
The present invention is directed toward improving two aspects of the topical ophthalmic use of betaxolol. First, the duration of action of the hydrochloride salt of betaxolol is approximately 12 hours, which means that a glaucoma patient must administer drops of an ophthalmic solution containing this form of betaxolol two or more times per day to the affected eye(s). The duration of action of betaxolol hydrochloride is believed to be directly related to the high aqueous solubility of this compound, which results in relatively rapid removal of the compound from the eye via the normal bathing of the eye by tears. It is therefore desired to provide a different form (i.e., salt) of betaxolol which is not as prone to this "wash out" effect, and as a result has a longer duration of action than betaxolol hydrochloride.
A second aspect of the current glaucoma therapy with betaxolol hydrochloride which the present invention is directed toward improving is the elimination of a stinging sensation experienced by some patients upon topical application of this form of betaxolol to the eye. This stinging sensation, although experienced in a minority of the patients treated, may interfere with a patient's compliance with prescribed therapy. The provision of a different form of betaxolol which has a therapeutic effect substantially equivalent to or better than that of betaxolol hydrochloride, but which does not cause a stinging sensation upon topical application to the eye, is therefore desired.